In a final stage of printing or copying in image-forming apparatuses such as an electrophotographic copying machine, a facsimile, and a laser beam printer, a heat fixing method is generally employed in which a fixing belt heated by a heating source is brought into contact with a pressure roller under pressure, and a transfer-receiving material having a transferred toner image thereon is caused to pass between the fixing belt and the pressure roller to melt unfixed toner by heating. The fixing belt used in this stage requires, for example, elasticity and thermal conductivity to obtain good fixability, and a mechanical strength to obtain good durability and good wear resistance. In order to prevent offset (double transfer) and the like and to form a clear image, the fixing belt further requires a good property of releasing a toner (i.e., releasing property) and a property that electrostatic charging does not tend to occur and electrostatic charge is easily eliminated.
As a fixing belt that satisfies these various requirements, a fixing belt (fixing roller) having a structure including a tubular base composed of a metal, polyimide, or the like, a resin layer (surface layer) composed of a fluororesin or the like having a good releasing property and good wear resistance, and a primer layer disposed between the base and the surface layer has been proposed. Furthermore, for example, in order to improve fixability of a color toner, a fixing belt (fixing sleeve) having a structure in which an elastic layer composed of silicone rubber or the like is further provided between a base and a surface layer, and primer layers are provided between these layers has also been proposed.
In addition, for example, in order to suppress electrostatic charging and easily eliminate electrostatic charge and to prevent offset and form a clear image, a method for imparting electrical conductivity to the primer layer, and a method for providing an electrically conductive layer have also been proposed.
For example, Japanese Patent No. 3305467 (PTL 1) discloses a fixing tube (fixing belt) including an electrically conductive primer layer or an electrically conductive layer containing 1% to 40% by weight of a carbon (carbon black) powder. Similarly to a primer layer of a common fixing belt, the electrically conductive primer layer in PTL 1 has a function of a bonding layer that bonds a fluororesin film serving as a top coat (surface layer) and a polyimide tube serving as a base. However, by incorporating a carbon black powder, electrical conductivity is imparted to the primer layer, and thus the electrically conductive primer layer has also a function of an electrically conductive layer for preventing offset and forming a clear image.
PTL 1: Japanese Patent No. 3305467